x86/svm: Correct vm_event API for descriptor accesses

x86/svm: Correct vm_event API for descriptor accesses

c/s d0a699a389f1 "x86/monitor: add support for descriptor access events"
introduced logic looking for what appeared to be exitinfo (not that this
exists in SVM - exitinfo1 or 2 do), but actually passed the exit IDT vectoring
information.  There is never any IDT vectoring involved in these intercepts so
the value passed is always zero.

In fact, SVM doesn't provide any information, even in exitinfo1 and 2.  Drop
the svm struct entirely, and bump the interface version.

In the SVM vmexit handler itself, optimise the switch statement by observing
that there is a linear transformation between the SVM exit_reason and
VM_EVENT_DESC_* values.  (Bloat-o-meter reports 6028 => 5877 for a saving of
151 bytes).

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Alexandru Isaila <aisaila@bitdefender.com>
Acked-by: Adrian Pop <apop@bitdefender.com>
Acked-by: Jan Beulich <jbeulich@suse.com>